The present invention generally relates to hardcopy apparatus, such as copiers, printers, scanners, facsimiles, and more particularly to improved media holddown devices for such apparatus.
Hardcopy apparatus and particularly in apparatus handling media of big size, such as large format printers, are supplied by moving the end of the printing media manually towards the input portion of the apparatus, the printing media usually being a roll of printing media or sheet of printing media or the like, the printing media being pushed manually until its front edge is gripped between the feed roller and the drive roller which advance the sheet or the roll.
A problem which frequently arises in apparatus of this type is that, given the manual guidance of the printing media has to be carried out at a considerable distance from the front edge of the printing media, it is difficult to achieve good alignment of the printing media and , in many cases, this delays the operation of the printer when this operation has to be repeated, since the printer cannot tolerate appreciable deviation of the printing media from the theoretical position.
As is clear, the need from a repetition of the said loading operation results in loss of time.
Furthermore, a feeding operation of a printing media not properly positioned may result in a paper jam, with a consequent loss of paper, which may be very expansive depending on its size and quality, as well as in a further loss of time for removing the paper jam.
Alternatively, an improved method of loading media into a printer is disclosed in the European patent application no. 97 500153.8. In this application the method of loading the printing media into the printer provides for the operation of the rollers for advancing the printing media to be activated manually by the operator himself at the moment when the said printed media is introduced into the printer and at the moment when the operator estimates that the sheet of printing media is correctly positioned, without deviation.
However, also in this case manual loading and positioning of media appears to be cumbersome, in particular when cut sheet of media are employed. In fact it is still difficult to achieve good alignment of the printing media since few references are provided to the operator in order to estimate if the media is correctly positioned or not.
Finally, both the solutions cause a sharp change of status of the media, i.e. from completely free to stably locked. This change may cause an unintentional modification of the position of the media, which may result in an incorrect feeding of the sheet into the printer.
Conventionally, sheet holddown devices such as electrostatic or suction devices are employed only to reduce the effects of paper curl and cockle on dot placement during printing. In vacuum holddown devices, sheet flatness is maintained by providing suction between a support plate and the back surface of a sheet to be handled.
Cockle effect is the reluctance of the paper to bend smoothly. Instead it bends locally in a sharp fashion, creating permanent wrinkles.
Although conventional vacuum holddown devices are fairly effective in maintaining sheet flatness during printing, they have drawbacks. One drawback is the complexity of maintaining the same holddown force along the entire width of the medium while printing, i.e. in the direction of the printheads motion. This is due to the losses of air that the conventional devices allow, causing the medium to be subject to different forces, i.e. forcing the medium to rotate while it is advanced in the direction of the media motion.
Another drawback is that on one hand the maximum holddown force on a sheet is limited because of the necessity to maintain low frictional loads on transport devices which index the sheets. In conventional inkjet printers, such limitations can cause pen-to-sheet spacing distances to vary from swath to swath. Consequently, the holddown pressure at a localised area being printed may be insufficient to flatten cockles and other paper irregularities. On the other hand the vacuum required to eliminate cockle wrinkles in a printout would be so high that is normally unfeasible; in fact, high vacuum may suck the ink right through the paper and at the same time generate a lot of noise.
Applicant has then experimented that the employment of a vacuum holddown input unit may help media to be properly manually positioned by the operator.
The present invention seeks to provide an improved hardcopy apparatus and method of loading a printing medium in the hardcopy apparatus.
According to an aspect of the present invention, there is provided a hardcopy apparatus comprising a main roller and a loading mechanism to load a medium into the hardcopy apparatus, said loading mechanism comprises a vacuum holddown input unit to hold media down onto a surface of said holddown unit.
This reduces the risk of any unintentional modifications of its positioning. In fact the medium always stays in a sort of partially bounded condition, i.e. it is stably held, unless a significant force is applied in order to have it moved, since the vacuum is not switched off during the positioning operation. It should be noted that, direct contact of the holddown device with the printing surface is avoided to minimize signs and other adverse affects on print appearance.
Preferably, said holddown unit comprises a vacuum source, connected to atmosphere through a plurality of first apertures formed into the surface, and a vacuum channel to generate a negative pressure capable of holding down media onto the surface, while loading a medium.
In a preferred embodiment, said surface further comprises a plurality of recesses, at least one of said plurality of first apertures is located in one of said plurality of recesses.
However, the air flow between the surface and the back of the medium may generate noise in correspondence of the first apertures.
Accordingly, in a preferred arrangement, at least one of said plurality of recesses comprises a first portion capable of uniformly distributing the vacuum on an area substantially bigger than the aperture itself, and a second portion so shaped to reduce air flow noise interference with media.
This result is achieved since the shape of the recesses is designed for providing the air flow with a smooth transition, reducing the resulting noise.
Typically, said holddown unit further comprises a plurality of second apertures formed into the surface to create an additional negative pressure capable to increase the stability of media onto the surface. Advantageously, said holddown unit further comprises means to extend the additional negative pressure to a position closer to the drive roller.
This feature allows the media to be loaded in a position closer to the drive roller, reducing the distance to be covered during the feeding operation to engage an edge of the medium with the drive roller.
Preferably, said means for extending the negative pressure comprise a plurality of grooves extending towards the drive roller and a number of said plurality of second apertures are located within said grooves and each aperture (330) of said plurality of second apertures being located within a groove.
In a further preferred embodiment, said holddown unit further comprises feeding means, being the generated negative pressure capable to engage the back of the medium with said feeding means and transfer said medium to engage said drive roller.
Accordingly, the apparatus may be kept free from any additional elements which may reduce the operator""s access to the input surface, reducing the complexity of his manual activity.
Additionally, said feeding means comprises one or more overdrive wheels disposed to form on the surface an alternating sequence of recesses and overdrive wheels in the direction perpendicular to the direction of motion of media.
In a further preferred arrangement, the holddown unit further comprises a first reference for placing the medium in a correct position on the surface, said first reference crossing the surface in the direction perpendicular to the direction of motion of media and a second reference for placing the medium in the right position on the surface, said second reference crossing the surface in the direction of motion of media.
Thanks to the input surface mainly free of obstacles the operator can be provided with a full visual control of a plurality of references, to help him in positioning the medium.
Preferably, said first reference is tangent to the portion of the grooves closer to the main roller. In this way, one edge of medium can be positioned at the very limit of the area capable of applying vacuum to the back of the medium.
More preferably, said medium is a cut sheet of media.
Viewing another aspect of the present invention, there is also provided, a method of loading a medium into a hardcopy apparatus including a holddown unit provided with a vacuum source, a main driving roller and a secondary roller, which comprises the steps of: manually positioning the medium onto a surface of the holddown unit; by rotating the secondary roller, advancing the medium towards the main roller; and engaging the medium to the main roller.
Preferably, the step of keeping the vacuum source activated during all the previous steps, in order to achieve the engagement of the secondary roller with the back of the medium.
In a preferred embodiment, the hardcopy apparatus further comprises one or more wheels, while the step of advancing the medium comprises the step of moving the one or more wheels clockwise or counter-clockwise, depending on the advancing direction of the medium.